The present invention relates generally to radar antennas, and particularly reflector radar antennas.
The use of Flanking-beam Array Switching Technique (FAST) in combination with a phased array radar antenna is generally well known. Phased array antennas include multiple radiating elements, such as slots. These elements are typically configured in a planar construction and are individually controllable in phase and amplitude. U.S. Pat. No. 4,675,681, entitled xe2x80x9cROTATING PLANAR ARRAY ANTENNAxe2x80x9d, issued Jun. 23, 1987 to Richard Kinsey (the ""681 patent), teaches one such antenna. The entire disclosure of the ""681 patent is hereby incorporated by reference herein.
FIG. 1A illustrates one face of a dual face FAST (Flanking-beam Array Switching Technique) antenna system of the type for use, for example, on ships according to the ""681 patent. The antenna 20 includes a pair of arrays 22, 24 each having a plurality of waveguides 26 arranged in parallel fashion and extending generally horizontally. Each array is made up of a plurality of slotted waveguides, preferably made of rectangular, thin walled aluminum. The waveguides may be supported by a grid of vertical 28 and horizontal 30 rectangular structural tubes. The waveguides are mechanically fastened to the vertical tubes 28 which are supported by the horizontal tubes 30. The horizontal tubes are mounted upon a dual A-frame structure 32 fabricated from structural aluminum I-beams. Each array is shown mounted in a tiltback angle of approximately 20 degrees relative to the vertical axis 34 of the support structure 32. An azimuth motor 38 is mounted upon the support structure to drive the antenna in azimuthal rotation. Roll motors, one of which is shown at 40, stabilize the antenna about the roll axis which is perpendicular to axis 34, by controlling the ballscrew assembly 42, using roll position signals provided from the ship""s gyro repeater (not shown). A housing 43 provides environmental protection for the antenna components located at each end of each array. A radome 60 comprising a planar sheet of epoxy glass or a similar material resistant to weather damage and transparent to the RF signals transmitted by the antenna is attached to the aperture face.
FIG. 1B illustrates a schematic view of a bi-directional FAST feed system suitable for use with the antenna of FIG. 1A. A pair of adjacent waveguides 100, 102 are shown schematically as having slots 104, 106, respectively, offset by one-half the slot spacing. An excitation source 108 is connected to one end of each of the waveguides and coupled through phase shifters 110, 112 to supply phase controlled power to each of the respective waveguides. The excitation source 108 is. also connected to hybrid load 118. An excitation source 126 is coupled through phase shifters 128, 130 to waveguides 100, 102, respectively, and is connected to hybrid load 132.
Using the bi-directional feed, two beams 120, 122 (FIG. 1C) can be formed simultaneously from one slotted waveguide 100 when excited using excitation source 108. The excitation source 126 produces a pair of beams 134, 136 (FIG. 1C) at the mirror image positions of the beams 120, 122 produced by source 108. Thus, as is illustrated in FIG. 1C, a total of four possible flanking beams for each array aperture are generated. Each of the beams can be electronically scanned in elevation by computer control of the phase shifters to provide surveillance of an area from 0 to 60 degrees or more in elevation with each rotation of the aperture.
There are known applications for radar antennas and systems which require relatively small and relatively low-cost packages. However, a realized drawback of a FAST antenna system is their relative bulkiness and undesirable high cost. Accordingly, it is an object of the present invention to provide a relatively low-cost and compact antenna system utilizing the FAST.
A radar tracking antenna system including: a parabolic-cylinder reflector; and, a subset of Flanking Beam Array Steered Technique (FAST) line feeds coupled to the reflector as a feed assembly.